Simulated cross-bridge patterns corresponding to ciliary beating in Paramecium

Abstract

It is generally accepted that bending of a cilium is caused by active sliding between outer doublets in the cilium produced by ATP-driven activation of their dynein–tubulin cross-bridges^1–3. Changes with time in the location and extent of the active sliding regions in the outer doublets are thought to be primarily responsible for the changing shape of a beating cilium. However, using conventional techniques of biochemistry and electron microscopy, it is difficult to identify the regions on the outer doublets where active sliding occurs⁴. Here we have used computer simulation of the beating of a cilium to investigate changes in the distribution of activated cross-bridges, and hence of active sliding, in the nine outer doublets. Hereafter, the pattern of this distribution will be termed ‘cross-bridge pattern’. Published data have indicated that there is a periodically changing series of cross-bridge patterns in the nine outer doublets. On this assumption, the computer mimicked relatively well the beating of a cilium of Paramecium in media of both normal and high viscosity. The computer also simulated flagellar-type beating⁵, in which the cross-bridge patterns were modified slightly.